Hydraulically operated machine tool



May 30, 1944 P. G. coRlN 2,349,846

HYnnAuLIcALLY-orERATED MAcHINE TooL Filed 001'.. 5. 1942 8 Sheets-Sheet 2 fff I'. i1, l

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rma/VE x May 30, 1944. P. G. coRlN HYDRAULICALLY-OPERATED MACHINE TOOL Filed Oct. 5, 1942 8 Sheets-Sheet 4 P. G. coRlN 2,349,845 4mrDmJJLICALLY-OPLRATED MACHINE TooL Y May 30, '1944.

s sheets-sheet s Filed oct. 5, 1942 Arron/Vex May 30, 1944. P. G. ,conm

nYnAULIcALLY-QPERATED nAcHINE -TaoLi Filed Oct. 5, 1942 8 Sheets-Sheet 6 I /N VE N TOR* May 30,' 1944. l P, G, om 9' 2,349,949

HYDRAULICALLYiOPERATED MACHINE TOOL v Filed'oct. 5, 1942 s sheets-sheet? May 30, 1944. `|=.v G. coRlN HYDRAULICALLY-OPERATED MACHINE TOOL` Filed oct. s, 1942 B Sheets-Sheet .8

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Patented May 30, 1944 HYDRAULICALLY OPERATD MACHINE TOOLV Philip Grosvenor Corin, Harrogate; England, assignorof one-half to IVIenryBerry" &' Company Limited, Leeds, Yorkshire, England Application October 5, 1942 Serial No.` 460,778 In Great Britain July 14, 1941- 6- Claims. (Cl. S04-28.1)

This invention relates to hydraulically-operated machine tools. It will be described with reference to it'sincorporation in a machine-for cutting internal longitudinal grooves or splines in hollow cylindrical elements (for example,` a inachine for` cutting the taperedsplines in the bore of a gun-buffer cylinder) but it is applicable also to other machine tools. of a reciprocatory type.

A-,machine tool according to this invention has a', driving cylinder and ram,.which arer connected respectively' to theJ worlr` and to the tool holder or other reciprocatory Work-engaging part ot the machinew (or viceversa), has. a continuous output rotary pump to supply'the necessary fluid pressure to the cylinder and ram for driving, purposes, and is' characterised by a choke. valve-to regulate. the. rate of. flow` of uid from the pump toathe: driving, cylinder and ram-i and by a loaded relief valve to allow the surplus flowfrom the pump to be `lay-passed.` The arrangement is such that the speed` oi the,y drivingram (or cylinder) may bevaried by varying. the ratez offlow oifluid fromv thel pump to the driving cylindenand the relief valve-is. set to open at a pressure below that at which.y the eiiiciency` curve of the, drive would,` begin to fall quicklyl owing to slip in the pump;

The said choke valve.y may be adapted to be manually operatedY whenever necessary,` and4 to remaininzany setposition until: moved therefrom manually; or: may be; arrangedfor automatic operationat regular'intervals, against spring. pressure or the like (say at the end` of every return stroke of the-` machine), in. which casa, locking means will be provided to1holdthe1valve.in the re-set position .whena changexofzspeedis effected.

Alternatively, the choke valvefcould: beadapted fory operationv automatically atY predetermined times, say atterra;v given number of strokesof the machine, or when the tool has. beenl adwill bezoperated by azpilotvalveor tappet valve, whosemovements are effected by contact with a memberreciprocating with` the driving ram (or cylinder), wherebyy automatic reversal of. the drive is effected at theend of each stroke. Stoppagefof the machine is effectedby stopprlethe ,740' vanced: to` certain limits,` such automatic: oper` motor, or by complete closing. of' the choke valve.

When itis desiredlthat the reciprocating part of the machine (e. g., the tool bar in the example cited) shall have an accelerated return stroke, this' may be effected by having different areas of thrustsurfaceto receive the driving fluid for the forward and reverse movements, and/or by having. different pressures of fluid at the opposite ends of the driving cylinder. In some cases, the main. thrust,.for the cutting stroke, may be imparted tothe solid outer end of a hollow ram, and the return thrust be imparted to the bottom inner end of the recess in the ram, the pressurefor thereturn thrust preferably being greater thanl that for themainthrust. Provision may bamade for tripping the automatic reversing mechanismv at either endA of the stroke, so that thel tool may be run, out, clear of the work, for inspection and other purposes.

According to afurther.feature` of the invention, as applied to the. grooving ofarticles which have an external flange, with a number of recesses. thereimagreeing with the number and position. of the internal splines, means is provided.. for locating4 the articles in thefwork-holding.. clamps. by means of such external recesses, so that, a. constant relationship obtains between the path of the tool'. andsuch recesses. Where there-aref no, such. recesses, a sleeve or collar may be clamped` on to the cylinder, itself having locating recesses, andV this will remain on the cylinder Iuntilithe machining is finished. By either of thesemeans it` is. possible, lfor instance, to roughmachine a set of gun-buffer cylinders or like articles, each in the three or other number of `placeswith. the-cutter moving at a higher speed, and then tol go through the set again, after changingy the cutter, to .finish them with the machineworking at alower speed (because of operation` of the said choke valve), and the operator can be sure thatin every case `the cylinder is ,positionedin ythe correct angular and longitudi'nalA relationship with the tool path. For articles which do not have external formations which can be used for aligning, the internal grooves, clamping. and positioning means other than the attached sleeve on collar maybe adopted.

The machine may include automatic tool-advancing means, e. g., a ratchet and pawl mechanism, operated. atthe end of each forward or return stroke, and such means may include an .auifomaticv stop mechanism to operate when a predetermined,` feed vhas. been made. Such a stop A mechanism "could include an abutment to limit the total feed of the tool, and a collapsible such switch mechanism may merely actuatea.

signalling device to indicate to the operator that the cutis finished. The invention also comprises a cutter bar off'i.Y the type having a feed Cam .t yIlle adyanced stepby-step behind a spring-retractable,cutter.. in i.

which a roller is provided between the vfeed .cam

and the copy bar, behind the cutter, Vin v.which z the feed cam is hinged at a point remote from the cutter, and in which the cutter itself is loosely mounted on its pivot so as to clear itself;

at the commencement of the return stroke.

Finally, the invention' may be characterised by the particular constructionalembodiment described below with reference to' the accompany- 'ing drawings. Y

In the accompanying drawings, an example of machine according to this invention is illustrated, the machine having been designed-for the cutting of tapered longitudinal vsplines in a gun-buffer cylinder: f

Fig. 1' is afront elevation of the machine'with the front cover and control panel in'position;

Fig. 2 is an end view of the'same; fand Fig. 3 is a plan:

Fig. 4 is a front elevation with the frontcover and control panel removed' to show the pumpjthe control cylinder and the associated hydraulic driving means. YIn this figure the uppervparts of the machine, including the cylinder` to be grooved, are shown in section; f y

Fig; 5 is a transverse section, also showing the hydraulic driving means: Y

Fig. 6 is a further but fragmentary front' elevation, also with the front cover vand control panel removed, but showing vthe automatic reversing mechanism, and thetrip means `forrunvning the machine out or in at the end of its normal stroke.v The parts areshown run right in, beyond the normal point of reversal. j Fig. 7 is a transverse section through the machine showing the reversing mechanism of Fig.6 in'end elevation:

Fig. 8 is aV longitudinal vertical section- (to a larger scale) of the hydraulic control cylinder shown in Fig. 6; and f Fig. 9 is a transverse section of the same (also to a larger scale) taken on the line'Q-S of Fig. 8.

Fig. 10 is a longitudinal verticalv section (to la larger scale) through'the cutter bar. the cylinder to be grooved and the hydraulic driving cylinder, the cutter being shown in the innermost ready for a cutting movement; f

Fig. 1l is a detail section (also to a'larger scale) through the copy bar holder hereinafter described: p

Fig. 12 is a vertical section, and

Fig. 13 is a plan of the means shown in Figs. 1 and 2 for advancing and limiting thefeed of the cutter; and

Fig. 14 is a partly-diagrammatic representation of one means of indicating the completion' of a cut.`

As shown, more particularly in' Figs. 1 to 5,` the machine comprises a'4 rigid, metal, trough-like table or stand I mounted on'suitable'supports 2,

position,

on which table, near one end, is secureda head- '-'75 ing from its outer end. The mouth of this recess has a gland 8a, and slides over a hollow rod 8b l extending from the bracket 5. The said outer `end of this rain I is coupled by means of the bracket 9 to theboring bar hereinafter described ',in detail,` that bar being disposed horizontally :above and` parallel with the ram l.

Beneath the table I is mounted an electric motor I0 (Fig. "4), driving by means of chain or belt Illa, a-continuous-delivery rotary pump II.

. Also, beneath the table is mounted a control cylinder I2, which latter (as is shown in greater detail in Fig. 8) has two parallel longitudinal bores I3, I4, thefone I3 containing a Boating pistonor shuttle I5 and the other :I4 containing a positively-actuated pilot piston I6. The bore I3 is partly encircled by and communicates with a pair of arcuatev passages Il (see Fig. 9), one of which communicates with anv inlet port I3 to which the delivery pipe I9 from the pump II is connected, and the other of which communicates with a port to` which the exhaust pipe20 leading -to the supply .tank 2| is connected. Branching from the exhaust pipe 20; and projecting through the control panel on'the front of the machine is the filling nozzle 22. The said passages I1 communicate with Athe bore I3 by rneans of the radial holes 23 (see Fig. 9) at a point wheresuchholes are-under the control ofthe shuttle I5, and they also communicate with the bore I 4a at a point where they are under the control of the piloti valve I6.. The bore I4 also has a constant pressure inlet I2a as shown in Fig. 4,

'branching from the said delivery pipe I9. .The varrangement is, such that, in one end positionof the pilot valve I6 pressure fluid drives the floating rpiston I5 to oneend of its bore I3. to admit Ipressure fluid t0 the driving end of the driving cylinder; and in the other end position of the pilot valve I6, pressure fluid drives the floating piston I5 to the other endof its bore I3 to exhaust the driving end of the driving cylinder.

`stoppage of the machine may be effected either -by stopping the motor I0, or by means of the choke valve now to be described.

In the feed pipe I9 which leads from the deliv- `ery side of thepump II to the control cylinder I2, is arranged a choke valve 24 which, on being partly rotated, by .means of handle 24a` on-shaft 24h, reduces the orifice through which the fluid can ow, or substitutes a smaller rfor alarger orifice, as the case may be, and thereby reduces the rate of fiow offsuchiluid tothe cylinder I2.

y'Between such choke valve 24 and the pump II,

branches a spring-loadedrelief Valve 25, the rear .side-of which communicates through another conduit 26 with the supply tank 2l from which the pump I I draws its fluid. The said choke valve 24 is provided with the handle 2Ml which cooperates With stop means so that it may be thrown between `two extreme positions to effect the `fast or slo'w delivery, as desired. Also extending from .the delivery pipe. I9 is a constant-pressure pipe -28 leading to the outer end of the said hollow rod .8b and-'supplying the` pressure for the 'return strokeoffthe raml.V 'In this pipe v28 is a further choke valve 28a (which is notaccessible through screwing `at 4'8- into `a rotary nut 49.

the control lpanel) 'bywhichthe rate of flow to tlliefr'am 'l maybe'initiallyadjusted. @The smaller pipe "29' leads to"thepressure gauge 30 on the control" panel; a "When movement of the control valve 24 merely varies the" size of the'through orifice, as distinct fromsubstituting a larger or smaller orifice, the stopj' means Vmay be adjustable so as to vary the ratesA of riowat'the' two extreme positions. Also therelmaybe' separate means, 'such as a second handle on the valve; or a separate valve, for complete "closingof' the' pipe I9 to stop the machine. Extending'from lsaid pilot valve I6 is along tappetV rodhavingad-justable stops 32, 33 1ther`eon,=wlf1ilst depending from the driving ram 'I'isaflu'g 34 carrying apivotally mounted'tappet "35'V adapted to engage therespective stop 32er {s3-*attire ends of its stroke, to displace the pilot valve ljin its `bore and effect reversal of the driving ram inthe manner explained above.

' A'Iheftappet35 extends forwardly beyond the 'tappe'trodv 3|, and overlies a lifting bar 3E carried inlinks-31pivotally mounted in the xed bracketsfS below the table I, and' one of such 'links is connected'by4 a short member 33a to a hand-le v(tipi-voted at 4t and extending forwardly through the control panel. The depression of thehandleB-S causes the lifting bar 3B to raise the tappet clear of the stops 32 and 33, whatevei` the position'of `the ram 'l in the cylinder E, so that the ram 1 will then move to the extreme end of its stroke and remain there. The manual operation of tappet rod 3l is described *belowf As willl be seen inL Fig. 6 `the ram has has 4been run right in, the tappet 35 having been lifted over the stop 32; The stops 32 and 33 are backed-off so that tappet 35 will ride over them in one direction.

The boring tool (see Figs'. 4 and 1G) comprises `anelongated tubular carrier member 4l, a Y pivotally-mounted tool 424 at one end, with a spring 43 tending to Withdraw the tool from its cutting position, a feed cam 44 behind the tool 42 to`l advance it-to the cutting position against 'the-pressure ofAv the springy 43, screw means 44a -at one `end of the'bar for advancing the feed cam 44-to obtain progressive advancement of the tool 42,v anda prole bar VL45 governing the feed positionl oi"l the `tool` during its reciprocatory motion.

lThe feed cam 44 is formed on the end of a long bar 4t, hinged at '4-1, remote from the cutter and Housed above the 'feed camV 44- behindthe Workingl edge of the cutter,l is a rol-ler50 mounted on pin 51 soifas to ride'on` the `copy bar 45; which bar is held by screws 52, inashaped holder 53 carried rby the Xed bracket 54'.l "A compressionv spring Sbelowthe bar 46 holds the roller 50- against the copy bar 45.

'-`I"lie gun-buffer cylinder 56 which is to be grooved is housed at one end in a bearing 51 between which and the cylinder yis a tapered clamping member 58 in a collet member 59, and is 'housed at the other endin. a bearing 53 having a hinged cap 60a.- To thislast namedv bearing fandlcap is yiitted a detachable quick-release cou- Afpling t2 for the hoseA of a coolant circuit the coolant. flowing throughthe cylinder into the `trough .I, andtothe circulating pump 6l. They `pump BI supplies the coolant to the tool through the ilxedpipe 61a, adjustingl valve Stb, and flexiblepipeila `A sump for the coolant is MshoWnLbelow the `pump 6|., complete with filter grid'anddrainoutlet.l '1 Y recesses 59a to receive'the plunger, which recesses are in the same'angular relationship as arethesplines. i r vvReferring now to` Figs.` l2 and 13, thel said rotary nut 49- carries-a bevel wheel 65 meshing with a further Abevel Wheel 66 on the axisyo'f `a 'hand wheel fil-,this gearing beingfhoused i-n a box- 68. f Pivotal-ly mounted on the far sideof the box, opposite pinion 65, is a plate 69 carrying two adjustable screws 16,111-, operated by 'knobs outside the box". By moving the plate 69 about its44 pivot; either-ofk these `screws may be placed opposite thejbar 46 to serve as a stop; so that one maybe usedto limit the rough cut, say at a higher' speed, and then the other be used to limit the nishingcut, sayv at a slower-speed. `A

lball andY spring detent device 'f2 serves to` locate the plate B9 in its two positions. l

Secured to the top of the box 68 is a bevelled disc 68a, havinga single datum# or Zero line marked across its bevelled face, Whilst immediately above such disc, and keyed to the axle 'of handwheel 6lv is a two-partbevelled disc 68D, having a scale engraved-on the bevelledface of its outer part,` This scale has 3l equally spaced, numbered, `larger markings and-eachv representing an advanceof .001 in the cutter,and smaller markings each representing an advance of .005" in the cutter; Between the inner part of the disc 68h and the fixed'd-isc 68a is a ring of Yfriction material 68o, whilst a nutSBd, and' spring Washer- 68e serve to" urge the friction.v surfaces together. l Y

The outer part of the disc 68D bearing the l,

' initial positionfof the handwheel.

i The handvlheel 61, or a member moving there'- with, may be` arranged to 'come into contact with a stop member v' atthe end of `each l alternate stroke, to obtainl an automatic step-by-step feed of the cutter, for example, by aratchetarrangement, and in such casefa friction clutch or other slip device will be adopted, to operate-When the bar is obstructed by oneof the screws 1U, 1I.

Fig. 14 shows in a partly diagrammatic form, onearrangement of electric signalling device, to Warn the 'operator When'theintended depth `of cut is reached. -As illustrated the rod 46 carries a contact element 46a adapted to bridge the contact pinsl 4Gb Vwhen the tool has been fed'to the limit. The pins 4Gb` are in series with the signal lamp 46c and the'secondary of a transformer 46d. There mayalsobea cut-out device tostop the motor lil when the contacts 46o` are'brd'ged by the element 46a; Whilst in Fig.' 14 only one stop is shown for the rod 46, there may be two as in Figs. 12- and 13y and each may have the contacts 4Gb. l

The` control panel shown in Fig. lA comprises the pressure gauge 30, the handle 24a for' operatingthe choke valve-24; the handle 391 for changing-over from automatic to-and-fro rmovement, to arun-out movement in-ei'ther direction;

l trol,v cylindery I 2.

ai stop-and-start switchJS for the motor Ill; the filling nozzle 22; a lever 'I4 for manually operating. ythe vtappet rod 3I, solas to obtain kmanual reversal of Athe machine at,` any,A time, this lever operatingv through,I shaft v.15, andradial arm I6 onthat shaft, and link'la, ys ecured to the tappet rod (see Fig. 6) a knob 'VI for a;regulating cock (not shown) for the pressure gauge; and an oil level gauge I8 to indicate the level of voil in the tank 2|. Below the panel is a knob 'I9 on the motor shaft, for use in inching the motor when required. Levers, 24a. and l'I4 movein an. oscillatory path, whilst lever 39 moves in atvertical path. y ,l

In the `operation of the machine, the buffer cylinder to be groovedis first placed in position with4 one end clamped in the colletmember 51 by means of packing ringj, and with its other end held inthe bearing 6D by means of the cap Iia. f The buffer cylinder :is indexed by the` plunger 63 falling into one of the recesses in the collet member 57. l, The ,quickrelease coupling v462 for the coolant uid is now attached to bearing 1.60 soas to feed coolant fluid to the interior of the cylinder, and `the adjusting valve (ill)` is opened, if not alreadyy open., 'I'he cutter 42 and the stops I and 'II having been setthe copy bar having Ypreviously been securedA in position, and the outer part ofthe discI 68h having been brought to the zerol position and locked by means of screw 68j, the machine is ready for use.

, Assuming, control ,valve 24 to be closed, and the cutter bar `(and ram 1 having been run in to the extreme inner position, the motor I9 is, now started by means of the push-button switchfl3, Awhereupon the driving fluid commences to'circulate through the pump II, conduits I9, therelief valve 25, by-pass 26 and tank 2l.` VAt the same time, pressure fluid is fed to the interior of the ram 1 via pipe 28 and valve 28a, which tends to keep the ram (andcutter bar)y at the innermost positionthe driving cylinder 6 being open to exhaustk through the con- The valve. 24 is now moved over to the open position, for fast operation, whereupon the driving fluid is fed forward to the ,control cylinder I2, which, however, is still exhausted by valve I5. The operator now moves lever 14 to displace the tappet rod 3l and pilot valve I6, which results in the'shuttle valve I5 .being displacedgbyadmitting,fluid to open the .driving cylinder y5 to the pressure fluid, the result beingthat theram 'I and with it the cutter bar, is advanced out of cylinder V6 and at the higher speed, the tool42 during this movement, cutting the inner wall of the bufercylinder under the influence ofthe copy barA 45. The tappet 35 rides over stop 32 and falls on to the tappet rod 3| between the two stops..Y As the parts reach the end of the outward strokethe depending ,tappet 35 meets the stop l32 on the tappet rod 31| andthereby displaces ythat rod and the pilot vvalve I6,l which immediatelyresults in displacement of. the shuttle valve I5 to the other end of vits bore `andexhausts thedriving cylinder 6. As thereiszayconstant supply of pressure fluid from the pump-.to the interior of the hollow ram "I,

,through pipe, 28 and valve 28a, the exhausting of, the driving cylinder Sresults in the ram 1 being returned into the driving cylinder, and

vthe, cutter` bar thereby returned into the work. fhiereturn movement continues until tappet 315 rfneets *stop 32 onthetappet rod 3I, thereby re- 9 turning. they pilot .valve I6 vto its original position )andreversing the ,positionpf ,the shuttle valve I5, 'so as again to `feed the driving cylinder and repeatl thegcycleo'f operations. This repetition is continuedgthe `operator advancing the tool by means of handwheel lI'I at the end of each return stroke, untilthe outer end of the feed bar 46 meets the stop l0, after which no further feedcan be effected. The `operator now moves `the handle 24d to'r'educ'e the rate of oW through `the choke valve 24 and also displaces plate 69, solas to bring stop II intoline with the feed bar in placev of stop 16. Thereafter, the advancing of the tool by means of handwheel 61 is done more carefully and in smaller increments to give a finishing cut, the machine now running at a slower speed. Alternatively, all the splines in a'cylinder or even in a number of cylinders could be rough cut before stops I0 and 'II are reversed, and if necessary a change of tool may be made before giving the finishing cut.

When feed bar 46 meets stop 1I, or if at any intermediate time the operator wishes to examine the work, the control lever 39 is depressed, so as to lift the relieving bar 35 and bring the tappet 35 out of the path of the stop 32, the result 25 being that the ram 'I is forced as far out of its 4machine may be varied as desired, from a mere crawl to the maximum possible and, in fact, the machine can usually be stalled anywhere, if necessary. At all times, surplus fluid from the pump (which is a continuous-delivery pump) is by-passed through the relief valve 25, such valve, as above stated, being so loaded as to open vjust before slip inthe pump would cause an un due fall in efficiency.

The formation of the control cylinder I2 with the arcuate passages Il and the plurality of openings between these passages and the bore I3 allows of rapid exhausting and supplying of the bore I3, whilst giving adequate support to the Vvalve I5, and as a result almost instantaneous reversal of the ram 'I is obtainable, regardless of the speed at which the machine is working.

When one spline in the buffer cylinder is nished and another is to be begun, the lever 64 is depressed to withdraw plunger 63 from the collet memberl 57, whereupon the cylinder is rotated until such plunger 63 falls into another recess in the collet member, after which the cutting operation is repeated for the second spline. The machine may, of course, be stopped at any time by means of the switch 13. The pump 6I for the coolant fluid is driven by its own motor,

' independently of the main drive.

`continuous output uni-directional pump to supply the necessary fluid pressure'to both ends of the cylinder for'the drive-the supply to the return end of the cylinder being uninterrupted; having valve means for interrupting the fluid lpressure to the working end of the driving, cylinder and for exhausting thatend vof the cylinder only when the pressure supply is cut off; having a choke valve to regulate the rate of flow of pressure fluid to the said interrupting devices and to the working end of the driving cylinder; and having a loaded relief valve placed so as to allow surplus fluid from the pump to by-pass the interrupter valve means and the choke valve, and to allow fluid from the return end of the cylinder to escape without passing through the pump.

2. A hydraulically-operated machine tool having a driving cylinder and ram for creating motion between the tool and the work, having a continuous-output pump to supply the necessary fluid pressure for the drive, having a choke valve to regulate the rate of flow of uid from the pump to the driving cylinder and ram, and having a loaded relief valve to allow the surplus fluid from the pump to be ley-passed, and wherein the flow of fluid to the respective ends of the driving cylinder is controlled by a shuttle piston valve in a control cylinder, which valve in turn is operated by a pilot valve connected with a tappet rod and controlled by the reciprocating parts of the machine, with means for releasing the tappet rod from the reciprocating parts when desired.

3. A hydraulically-operated machine tool according to claim 1, wherein the choke valve is adapted to be manually operated whenever necessary, and to remain in any set position until moved therefrom manually, and having automatic tool-advancing means operated at the end of each alternate stroke, with stop means to limit the total advance, and a yieldable or collapsible mechanism in the tool-advancing means to give way when the stop means is reached.

4. A hydraulically-operated machine tool comprising a trough-like table, a headstock thereon, a driving cylinder and ram in the headstock, a control valve below the headstock with a tappet rod extending therefrom, means on the ram for engaging the tappets for automatic operation of the control valve, a motor below the table driving a continuous-delivery rotary pump, means for supplying pressure fluid to the larger end of the ram through the control valve, and to the smaller end of the ram directly, and a choke valve in such means to regulate the rate of flow of fluid to the said larger end, with a spring-loaded relief valve to by-pass the surplus fluid delivered by the pump, such relief valve being set to open just before the eiciency curve would begin to drop due to slip in the pump.

5. A machine according to claim 2, wherein the hydraulic driving means comprises a continuousdelivery rotary pump, a choke valve to vary the rate of iiow of fluid from the pump to the driving cylinder, and a loaded relief valve to Dy-pass any surplus fluid delivered by the pump.

6. In a hydraulically-driven machine tool according to claim 2, a control cylinder having parallel bores for the said shuttle piston valve and pilot valve respectively, arcuate exhaust and delivery passages encircling the bore for the shuttle valve and extending alongside the bore for the pilot valve, and a series of radially-disposed through openings between the arcuate pas sages and the bore it encircles, with further openings between them and the other bore,

PHILIP GROSVENOR CORIN. 

